The contribution of solvent to nucleic acid base stacking is being investigated. Model systems include: (1) Planar dyes, (2) Single stranded nucleic acids, (3) Double helices, and (4) Double helices with non-basepaired ends. Methods employed include laser temperature jump kinetics, fluorescence detected circular dichroism, melting curves, and conventional circular dichrosim. The results will provide insight into the general principles which determine nucleic acid chemistry.